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A - MSRA Obstetrics [16] > [10] Diagnostic Tests for Fetal Abnormality > Flashcards

[10] Diagnostic Tests for Fetal Abnormality Flashcards

1
Q

What is the advantage of ultrasound in the diagnostic testing for fetal abnormalty?

A

They are non-invasive, and so there is no risk to the baby

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2
Q

Why is ultrasound a versatile investigation?

A

They may be offered to diagnose a wide range of conditions in the baby

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3
Q

When is the first ultrasound scan in pregnancy usually performed?

A

Between 10-13 weeks

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4
Q

What is the purpose of the 10-13 week ultrasound?

A
  • Diagnose pregnancy
  • Accurately determine gestational age
  • Determine viability
  • Determine fetal number
  • Detect gross fetal abnormality
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5
Q

Why is it important to accurately determine gestational age?

A
  • To allow intervention in post-maturity

- To allow accurate serum screening for Down’s

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6
Q

How is viability determined on 10-13 week ultrasound?

A

Confirm heartbeat, and exclude ectopic pregnancy and molar pregnancy

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7
Q

What is further determined if multiple pregnancy is found on 10-13 week ultrasound?

A

The chorionicity/amnionicity

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8
Q

How is gestational age determined on 10-13 week ultrasound?

A

Measurement of crown-rump length

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9
Q

When can the measurement of crown-rump length be used to determine gestational age?

A

Before 13 weeks

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10
Q

What are the alternative ways of estimating gestational age?

A
  • Bi-parietal diameter and/or head circumference

- Femur length

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11
Q

How can risk of Down’s syndrome be tested for on ultrasound?

A

Measure nuchal translucency

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12
Q

When is scanning for nuchal translucency best done?

A

10-14 weeks

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13
Q

When is the anomaly scan offered to pregnant women?

A

Ideally 18-20 weeks

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14
Q

What is the main purpose of the anomaly scan?

A
  • Reassure mother that the baby appears to have no gross structural abnormalities
  • Determine placental morphology and localisation
  • Confirm fetal growth is appropriate
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15
Q

What % of significant abnormalities will be detected by the 20-week screening scan?

A

50%

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16
Q

What should you do if a problem with the fetus is found on the anomaly scan?

A

Provide parents with options, e.g. termination, preparation

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17
Q

What is considered to be abnormal placental localisation on the anomaly scan?

A

If the placenta extends within 20mm of the internal cervical os

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18
Q

What should be done if the placenta extends within 20mm of the internal cervical os on the anomaly scan?

A

Another scan at 32 weeks should be offered

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19
Q

What will be done during the anomaly scan?

A
  • Assessment of growth
  • Look at head shape and internal structures
  • Look at other systems
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20
Q

What parameters are used for the assessment of growth in the anomaly scan?

A
  • Bi-parietal diameter
  • Head circumference
  • Femur length
  • Abdominal circumference
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21
Q

What other systems are looked at during the anomaly scan?

A
  • Spine
  • Abdomen
  • Thorax
  • Arms and legs
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22
Q

What is looked at with regard to the abdomen at the anomaly scan?

A
  • Shape

- Content at level of stomach, kidneys, and umbilicus

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23
Q

What is looked at with regard to the thorax at the anomaly scan?

A
  • Four-chamber cardiac view

- Aortic arch

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24
Q

What is looked at with regard to the arms and legs at the anomaly scan?

A
  • Three bones
  • Hands
  • Orientation of the feet
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25
Q

Are aneuploidy scans routinely performed?

A

No

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26
Q

Why are aneuploidy scans not routinely performed?

A

As many normal pregnancies may have some of these features, resulting in a high false positive rate

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27
Q

What is aneuploidy?

A

Abnormal chromosome number

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28
Q

What will pregnancies affected by aneuploidy have on ultrasound?

A

Sonographic markers

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29
Q

Other than ultrasound, how can aneuploidy be identified?

A

Triple test, maternal age, and NT measurements

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30
Q

What % of cases of aneuploidy will be identified by the triple test, maternal age, and NT measurements?

A

50-80%

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31
Q

What are the indications for an aneuploidy marker scan?

A
  • Family history of abnormalities, e.g. neural tube defects
  • Multiple pregnancy
  • Maternal diabetes or epilepsy
  • Recurrent miscarriage
  • Polyhydraminos
  • AFP abnormal
  • Oligohydraminos
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32
Q

What does Doppler ultrasound do?

A

Uses high-intensity sound waves to detect the blood circulation in the baby, uterus, and placenta

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33
Q

What is Doppler ultrasound used for?

A

High risk pregnancies where there is concern about the baby’s wellbeing

34
Q

Give 3 examples of where Doppler ultrasound may be used because there is concern about the babies wellbeing?

A
  • IUGR
  • Hypertensive disorders of pregnancy
  • Distinguish normal small fetus to the ‘sick’ small fetus
35
Q

Is Dopper ultrasound used routinely?

A

No

36
Q

What is the current role of Doppler ultrasound?

A

Optimising management, particularly timing of delivery

37
Q

What is chorionic villus sampling (CVS)?

A

An invasive diagnostic test

38
Q

What does CVS involve?

A

Sampling of the developing placenta late into the first trimester of pregnancy

39
Q

What is the purpose of CVS?

A

To allow examination of the fetal karyotype and/or genotype

40
Q

How can CVS be performed?

A
  • Transabdominally (most common)

- Transcervically (prior to 13 weeks)

41
Q

When is CVS used?

A

Usually reserved for women at increased risk of carrying a fetus with a chromosomal or genetic abnormality

42
Q

What is the advantage of CVS, compared to amniocentesis?

A

It can be performed earlier

43
Q

What needs to be considered when deciding between CVS and amniocentesis?

A

Any benefit of earlier diagnosis with CVS must be carefully balanced against the slightly greater risks of pregnancy loss compared with second trimester amniocentesis

44
Q

Are there significant differences in long-term health outcomes between children who have had CVS and amniocentesis?

A

No

45
Q

What are the indications for CVS?

A
  • Positive antenatal screening test
  • History of genetic or chromosomal abnormality
  • Familial chromosomal rearrangement
  • Biochemical or molecular diagnosis of familial genetic disorder
46
Q

Give an example of a positive antenatal screening test that would be an indication for CVS

A

Combined test for trisomy

47
Q

What can CVS not be used for?

A

To screen for structural problems such as neural tube defects

48
Q

Why can CVS not be used to screen for structural problems such as NTD?

A

Because they have no known metabolic or molecular basis

49
Q

What are the contraindications to CVS?

A
  • Active vaginal bleeding

- Infection

50
Q

What is the trans-cervical route of CVS contraindicated by?

A
  • Cervical polyps
  • Fibroids
  • Fundal placenta
  • Retroverted uterus with posterior placement of placenta
51
Q

When is CVS usually performed?

A

11 - 13+6 weeks

52
Q

What medication should be given before CVS?

A

Rhesus immunoprophylaxis, where appropriate

53
Q

How is the placental sample obtained in CVS?

A

Either by ultrasound-guided trans-abdominal needle, or ultrasound-guided cannula aspiration

54
Q

How long does it take for results to be obtained with CVS?

A

Within 7-14 days, although newer tests can reduce reporting time to 24-48 hours

55
Q

What are the risks and complications of CVS?

A
  • Sampling failure
  • Miscarriage risk
  • Amniotic fluid leakage
  • Vaginal bleeding
  • Sepsis
56
Q

What might cause sampling failure in CVS?

A
  • Lab failure
  • Mosacism
  • Ambiguous results
  • Insufficient sample
  • Maternal cell contamination
57
Q

What is amniocentesis?

A

An invasive, diagnostic antenatla test

58
Q

What does amniocentesis involve?

A

Taking a sample of amniotic fluid to examine fetal cells found in the fluid

59
Q

Who is amniocentesis used in?

A

Usually reserved for those women considered at high risk of carrying a fetus with a chromosomal or genetic abnormality

60
Q

What does the amniotic fluid extracted in amniocentesis contain?

A

Cells from the amnion and fetal skin, lungs, and urinary tract

61
Q

What can be done with the cells obtained in amniocentesis?

A

They can undergo chromosomal, genetic, biochemical, and molecular biological analysis

62
Q

Is amniocentesis used as a screening test?

A

No

63
Q

Why is amniocentesis not used as a screening test?

A

As it is an invasive test posing risk to fetus and mother

64
Q

What can the timing of amniocentesis be divided into?

A
  • Early
  • Mid-trimester
  • Third trimester
65
Q

What is considered to be early amniocentesis?

A

12+0 - 14+6 weeks

66
Q

Is early amniocentesis recommended?

A

No

67
Q

Why is early amniocentesis not recommended?

A

As it is associated with an increased risk of miscarriage and higher incidence of talipes

68
Q

What is considered to be mid-trimester amniocentesis?

A

15-18 weeks

69
Q

What is the most common timing for amniocentesis?

A

Mid-trimester

70
Q

Why might third trimester amniocentesis be carried out?

A
  • Late karyotyping

- Detection of fetal infection in P-PROM

71
Q

What are the most common indications for amniocentesis?

A
  • Positive antenatal screening test
  • Previous child with chromosomal or congenital abnormality
  • High risk features on history
  • Analysis to detect specific conditions
72
Q

Give 2 examples of positive antenatal screening tests that may be indications for amniocentesis?

A
  • Combined test for trisomy abnormalities

- Abnormal fetal anomaly scan

73
Q

What high risk features on history may be an indication for amniocentesis?

A
  • Parent carrying balanced chromosomal translocation
  • Risk of recessively inherited metabolic disorder
  • Mother carrying X-linked disorder
74
Q

Give 3 examples of specific conditions that can be detected by amniocentesis?

A
  • CF
  • Tay-Sachs
  • Congenital adrenal hyperplasia
75
Q

What medication should be given before amniocentesis?

A

Rhesus immunoprophylaxis, where appropriate

76
Q

Describe the procedure for amniocentesis

A

It should be performed under continuous ultrasound guidance. A spinal needle is inserted through the maternal abdominal and uterine walls into the pocket of amniotic fluid within the amniotic sac

77
Q

How much fluid is obtained in amniocentesus?

A

1ml per week of gestation

78
Q

What are the risks and complications of amniocentesis?

A
  • Discomfort (uterine cramping)
  • Vaginal bleeding
  • Amniotic fluid leakage
  • Maternal rhesus sensitisation in susceptible pregnancies
  • Amnionitis
  • Miscarriage risk
79
Q

What is the risk of miscarriage in amniocentesis?

A

Increased risk compared to background is 0.5-1%

80
Q

What should be considered when thinking about the miscarriage risk with amniocentesis?

A

The risk of miscarriage may be due to the pregnancy characteristics of women undergoing the procedure

A - MSRA Obstetrics [16] (61 decks)

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